Thermal insulation elements

ABSTRACT

The invention relates to thermal insulation elements comprising
         a) a covering layer having a thickness of from 0.2 to 1.0 mm,   b) at least one vacuum insulation panel located on a),   c) a further thermal insulation material,   d) a further covering layer.

The invention relates to thermal insulation elements comprising vacuuminsulation panels, refrigeration appliances produced from these thermalinsulation elements and a process for producing the thermal insulationelements and also refrigeration appliances produced therefrom.

Refrigeration appliances play an important role in many fields.Refrigeration appliances include, for example, refrigerators, freezerchests, upright freezers, cooling containers or superstructures ofrefrigerated vehicles. The refrigeration appliances usually comprise ahollow space surrounded by thermal insulation elements within which thematerial to be cooled being located. The thermal insulation elementsusually comprise two covering layers between which a thermal insulationmaterial, usually a rigid polyurethane foam, is located.

There is an ongoing need to reduce the energy consumption ofrefrigeration appliances. One possible way of achieving this is toreduce the thermal conductivity of the thermal insulation materialsused. One possible way of bringing this about is the use of vacuuminsulation panels, hereinafter also referred to as VIPs.

Thus, the energy saving potential when using VIPs is about 10-40%compared to conventional, closed-celled rigid polyurethane foams.

Such vacuum insulation units generally comprise a thermally insulatingcore material, for example open-celled rigid polyurethane (PUR) foam,open-celled extruded polystyrene foam, silica gels, glass fibers, loosebeds of polymer particles, pressed milled rigid PUR foam or semirigidPUR foam or perlite, which is packed in a gastight film, evacuated andheat sealed in so as to be airtight.

The use of VIPs in refrigeration appliances is known and has beendescribed many times. Thus, WO 97/36129 describes VIPs which have anedge length of at least 40 cm and can be installed in refrigerationappliances.

EP 434 225 describes VIPs and their installation in refrigerationappliances. Here, the VIP is arranged between the covering layers andsurrounded with foam.

WO 99/61503 describes VIPs which are installed in refrigerationappliances. Here, they are fixed to the side facing the interior of therefrigeration appliance by means of an adhesive and the hollow spacebetween the covering layers is then filled with a rigid polyurethanefoam system.

A further ongoing requirement is to reduce the usage of materials in theproduction of refrigeration appliances. The use of VIPs enables, owingto their lower thermal conductivity, a reduction in the thickness of theinsulation of the refrigeration appliances to be achieved. In this way,an increase in the interior space and thus the useful volume of therefrigeration appliances is possible at the same dimensions of therefrigeration appliance.

A further saving has been able to be achieved by reducing the thicknessof the covering layers. However, this is possible only to a limitedextent.

When filling the hollow spaces of refrigeration appliances with rigidpolyurethane foam systems, flaws and voids are usually formed. When thethickness of the covering layers is too low, these flaws show up on theoutside. This impairs the esthetics of the refrigeration appliances andis regarded as a disadvantage.

It was an object of the present invention to efficiently producerefrigeration appliances which have a low energy consumption and a highquality/defect-free appearance, are simple to produce and can berecycled without problems.

This object was able to be achieved by the thermal insulation elementsdescribed in more detail below, by means of which refrigerationappliances can be produced.

The object was able to be achieved by thermal insulation elementscomprising

-   -   a) a covering layer having a thickness of from 0.2 to 1.0 mm,    -   b) at least one vacuum insulation panel located on a),    -   c) a further thermal insulation material,    -   d) a further covering layer.

The covering layer a) can comprise metal, for example, steel sheet. Inanother embodiment of the thermal insulation elements of the invention,the covering layer a) comprises polymers, in particular thermoplasticpolymers. Preference is given to using polystyrene or ABS polymers aspolymers. As described, the metal covering layers have a thickness offrom 0.2 to 0.5 mm, preferably at least 0.25 mm and in particular 0.3mm, and not more than 0.4 mm. In the case of polymer, a thickness of0.7-1.0 mm is preferred.

Preference is given to at least 60%, particularly preferably at least70% and in particular at least 80%, of the area of the covering layer a)being covered with the vacuum insulation panel. Complete coverage of thecovering layer a) is possible, but it is not preferred because a fillingof the corners with foam should be undertaken to make the refrigerationappliances produced from the thermal insulation elements stable. Inaddition, it cannot be ensured that regions in which the vacuuminsulation panels abut and form hollow spaces which can also not befilled by the further insulation material c) are formed at the cornersor edges in the production of the refrigeration appliances.

The covering layer a) can be covered by a plurality of vacuum insulationpanels, but preferably by only one vacuum insulation panel. Here, thevacuum insulation panels preferably have an edge length of at least 40cm, preferably 60±20 cm×160±40 cm, and a thickness of at least 5 mm andat most 50 mm. The size of the vacuum insulation panels is preferablyadapted to the size of the refrigeration appliances and should, asdescribed, be such that at least 60% of the covering layer a) is coveredby only one vacuum insulation panel.

The advantage of using only one vacuum insulation panel b) per thermalinsulation element is, in particular, that the diffusion of water vaporand the thermal conductivity can be reduced as a result of the gap-freecovering of the covering layer a) and any gaps which can occur at theouter skin at the boundary between two vacuum insulation panels areavoided. Due to the size, this embodiment can be used, in particular,when the thermal insulation elements are used for producingrefrigerators or freezer chests.

The production of vacuum insulation panels and the materials used forthis purpose are known. As core materials, preference is given to using,as described, open-celled rigid polyurethane foams or foamedmelamine-formaldehyde condensation products.

A process for producing the foamed melamine-formaldehyde condensationproducts is, for example, described in EP 220 506.

The foamed melamine-formaldehyde condensation products can comprise upto 50% by weight of other thermoset formers which have been cocondensed.These are preferably condensation products of compounds comprisingamine, amide, hydroxyl and/or carboxyl groups with aldehydes, inparticular formaldehyde. Preferred thermoset formers are condensationproducts of substituted melamine, urea, urethanes, aliphatic amines,amino alcohols, phenols and their derivatives with aldehydes. Asaldehydes, it is possible to use, in a mixture with or in place offormaldehyde, further aldehydes such as acetaldehyde, benzaldehyde,acrolein, terephthalaldehyde.

Furthermore, the foamed melamine-formaldehyde condensation products cancomprise further additives such as organic or inorganic fillers. Asadditives, it is possible to use fibers, inorganic powders such as metalpowders, kaolin, quartz, chalk, further dyes and pigments.

Since the foamed melamine-formaldehyde condensation products have onlycell struts and no cell walls, they are very easy to evacuate.Preference is given to using rigid melamine-formaldehyde condensationproducts.

Foamed melamine-formaldehyde condensation products are known and aremarketed, for example, by BASF AG under the trade name Basotect®. Theyare usually produced by partly dissolving a pulverulentmelamine-formaldehyde condensation product in water comprising salts orsurfactants, mixing the resulting paste-like intermediate with a blowingagent, preferably in an extruder, and foaming the resulting product byheating, for example in a hot air oven. The foam can subsequently beheat treated in a heat treatment apparatus. Foaming is preferablycarried out in a temperature range from 120 to 180° C., and heattreatment is preferably carried out in a temperature range from 200 to250° C.

Suitable rigid polyurethane foams are described, for example, in EP1512707. In the production of the open-celled rigid polyurethane foams,water and/or hydrocarbons are preferably used as blowing agents.

In a specific embodiment of the invention, open-celled foams based onisocyanate having a cell size of less than 100 μm are used as corematerial of the vacuum insulation panels. Such foams can be obtained viaaerogels.

In the production of vacuum insulation panels using rigid polyurethanefoams, the foam is firstly produced in a manner known per se. The foamsobtained are then, if they have not already been produced as moldingshaving the desired size, are brought to the shape which they have ascore of the vacuum insulation panel. This is preferably achieved bysawing to the appropriate board size. The moldings are then packed inthe gastight sheathing, preferably the composite film, evacuated andheat sealed so as to be gastight.

It is usual for a getter material to be heat sealed in together with thecore material in order to prevent volatile substances which outgas laterfrom impairing the vacuum. Getter materials which can be used are, forexample, zeolites, activated carbons, strongly hygroscopic materials.

A film is generally used as sheathing material for the vacuum insulationpanels. Preferred films are composite films, in particular multilayercomposite films having a vapor-deposited or laminated-on metal layer,for example of aluminum. Suitable films comprise, for example,polyester, polyvinyl chloride, polyolefins such as polyethylene orpolypropylene or polyvinyl alcohol.

The use of open-celled rigid polyurethane foams as core material for thevacuum insulation panel is, as described, preferred. The advantages arefirstly that the refrigeration appliances produced in this way arecompletely recyclable since no constituents extraneous to the system arecomprised in the refrigeration appliance. Secondly, the boards can behandled more easily than pulverulent materials in the production of thevacuum insulation panels.

The vacuum insulation panels b) can be fixed to the covering layer a) bymeans of adhesives or adhesive tapes.

As described, the thermal insulation elements of the invention are usedpredominantly for the production of refrigeration appliances.Refrigeration appliances are, for example, refrigerators, freezerchests, upright freezers, cooling containers or superstructures forrefrigerated vehicles. The thermal insulation elements of the inventioncan be used both as wall elements and as door elements.

The refrigeration appliances can be produced in various ways.

In one embodiment of the production of the refrigeration appliances, thethermal insulation elements are produced separately as flat elements andare then joined to produce the refrigeration appliances. This embodimentis, in particular, preferred in the case of very large refrigerationappliances, for example cooling containers or superstructures forrefrigerated vehicles. Here, the covering layers a) and d) can be fixedin place with the desired spacing and the insulation material c) can beintroduced. As insulation material c), use is made of, in particular,rigid polyurethane foam whose liquid starting components are introducedinto the hollow space where they cure to form the polyurethane and atthe same time firmly join the covering layers a) and d) to one another.

It is in principle also possible to produce the thermal insulationelements by the continuous double plate process. For this purpose, thevacuum insulation panels b) are placed on the moving lower coveringlayer a), the liquid starting components for the rigid polyurethane foamare placed on these and the upper covering layer d) is then applied. Thethermal insulation element obtained can then, depending on the length ofthe vacuum insulation panels b) introduced, be cut between the vacuuminsulation panels b).

In the production of refrigerators or freezer chests, preference isgiven to molding the outer covering layer a) and the inner coveringlayer d) to form the housing of the appliance and to introduce theliquid starting components of the rigid polyurethane foam used asinsulation material into the hollow space between the covering layers.The rigid polyurethane foam firmly joins the covering layer and thusstabilizes the housing.

In one embodiment of refrigerators, insulation elements whose coveringlayer a) comprises cardboard or polyolefin, e.g. polyethylene orpolypropylene, are used for the rear side where aesthetic considerationsnaturally do not play a dominant role. Otherwise, these thermalinsulation elements have the same structure as described above.

In a further embodiment of the production of the refrigerationappliances, it is possible, as described above, for the thermalinsulation elements to be produced on a continuous double plate unitand, as described in EP 1 075 634, cut to length, mitered and folded toform the housing of the refrigeration appliance. Care has to be takenhere that the vacuum insulation panels b) introduced are not damaged.

The rigid polyurethane foams which are preferably used as insulationmaterial c) are preferably the customary and known compounds as aredescribed, for example, in Kunststoff-Handbuch, Volume 7 “Polyurethane”,3rd Edition 1993, Carl Hanser Verlag, Munich, Vienna. These compoundsare usually produced by reacting polyisocyanates, preferablydiphenylmethane diisocyanate and mixtures of diphenylmethanediisocyanate with polyphenylene-polymethylene polyisocyanates, alsoreferred to as crude MDI, with compounds having at least two hydrogenatoms which are reactive toward isocyanate groups. The compounds havingat least two hydrogen atoms which are reactive toward isocyanate groupsare usually polyether alcohols and/or polyester alcohols, preferablyones having a functionality of at least 3. The polyester alcohols areusually reaction products of polyfunctional carboxylic acids withpolyfunctional alcohols. The polyether alcohols are usually reactionproducts of compounds having at least 3 active hydrogen atoms withalkylene oxides, preferably ethylene oxide and/or propylene oxide. Ascompounds having at least 3 active hydrogen atoms, use is usually madeof polyfunctional alcohols such as glycerol, trimethylolpropane or sugaralcohols, preferably sucrose or sorbitol, aliphatic amines such asethylenediamine or aromatic amines such as tolylenediamine (TDA) ordiphenylmethanediamine (MDA), usually in admixture with its higherhomologues.

The reaction usually proceeds in the presence of catalysts, blowingagents and auxiliaries and/or additives. Water is usually used asblowing agent, most often in combination with inert compounds which areliquid at room temperature and vaporize at the reaction temperature ofpolyurethane formation, known as physical blowing agents. Customaryphysical blowing agents are alkanes, fluoroalkanes and methyl formate.Among the alkanes, pentanes and in particular cyclopentane have thegreatest industrial importance.

In the case of the rigid polyurethane foams used as core material forthe vacuum insulation panels, use is in principle made of the samestarting materials as for producing the polyurethanes used as insulationmaterials c). However, water and hydrocarbons, preferably cyclopentane,are predominantly used as blowing agent.

The advantages of the thermal insulation elements of the invention overthermal insulation elements without vacuum insulation panels are thesignificantly lower thermal conductivity, the lower gas diffusion andthe ability to reduce the thickness of the insulation layer and thussave material. The process of the invention surprisingly also makes itpossible to reduce the thickness of the carbon layer without thisresulting in disadvantages in terms of the aesthetics of therefrigeration appliances, the stability and the use properties. Inaddition, the residence times in the mold can be reduced by up to 50% asa result of decreasing the thickness of the remaining insulation layerc) when using rigid polyurethane foam as c) in an appropriate design.Furthermore, a more useful space can be made available by reducing thelayer thickness at the same external dimensions.

In the production of the thermal insulation elements of the invention,the temperature of the tool or the mold can be reduced down to 23° C.

1. A thermal insulation element, comprising: a) a covering layer havinga thickness ranging from 0.2 to 1.0 mm, b) at least one vacuuminsulation panel located on a), c) an additional thermal insulationmaterial, d) an additional covering layer.
 2. The thermal insulationelement according to claim 1, wherein the covering layer a) comprisesmetal.
 3. The thermal insulation element according to claim 1, whereinthe covering layer a) comprises a polymer.
 4. The thermal insulationelement according to claim 1, wherein the vacuum insulation panel b)comprises a core of open-celled rigid polyurethane foam which issheathed by a film, evacuated and closed.
 5. The thermal insulationelement according to claim 1, wherein the vacuum insulation panel b) isfastened in an adhesive manner to the covering layer a).
 6. The thermalinsulation element according to claim 1, wherein the vacuum insulationpanel b) covers at least 60% of the area of the covering layer a). 7.The thermal insulation element according to claim 1, wherein at least70% of the area of the covering layer a) is covered by a vacuuminsulation panel b).
 8. The thermal insulation element according toclaim 1, wherein the additional insulation material is a polymer foam.9. The thermal insulation element according to claim 1, wherein theadditional insulation material c) is a rigid polyurethane foam.
 10. Thethermal insulation element according to claim 1, wherein the vacuuminsulation panel b) comprises a core of foamed melamine-formaldehydecondensation product.
 11. The thermal insulation element according toclaim 1, wherein the additional covering layer d) comprises a metal or apolymer.
 12. (canceled)
 13. A refrigeration appliance, comprising: ahollow space which is surrounded by sheet-like thermal insulationelements, wherein at least one of the sheet-like thermal insulationelements is the thermal insulation element according to claim
 1. 14. Therefrigeration appliance according to claim 13, wherein the thermalinsulation elements are arranged so that the covering layer a) forms theouter surface of the refrigeration appliance.
 15. A process forproducing thermal insulation elements according to claim 1, whichcomprises: ai) fixing a vacuum insulation panel b) onto the coveringlayer a), bi) fixing the covering layer d), ci) introducing a liquidrigid polyurethane foam system into the hollow space formed in step bi),di) curing the rigid polyurethane foam formed in step ci).
 16. A methodof thermally insulating refrigeration appliances, comprising:incorporating the thermally insulating element according to claim 1 as adoor element or wall element in refrigeration appliances.